This invention relates to robust methods of frequency re-use and frequency sharing which prevent independent radio systems from co-interference due to frequency crowding of available radio bands, and, more particularly, this invention relates to a method of frequency agility which can provide a low cost solution to many burst mode and continuous data communications applications, including security systems, fire systems, access control, energy management, remote control of model planes, remote process control, traffic light control, remote power meter reading, voice communication, radio location, or local area networks.
The use of spread spectrum communications and techniques for diverse commercial and civilian applications has increased in recent years. By utilizing such techniques to minimize mutual interference and to provide anti-jamming advantages to multiple-access communications, as well as aiding in extremely accurate position location using satellites in synchronous and asynchronous orbits, spread spectrum techniques are known to offer the advantage of improved reliability of transmission in frequency-selective fading and multipath environments.
U.S. Pat. No. 4,799,062 to Sanderford, Jr. et al teaches that multipath in urban areas poses a problem for accurate position location, which may be overcome by using a method of synchronization of transmissions and unique identification codes to derive relative ranging times for determining position. Compensation for multipath may include spread spectrum techniques.
U.S. Pat. No. 4,977,577 to Arthur et al has a wireless alarm system using spread spectrum transmitters and fast frequency shift keying for achieving a coarse lock and a fine lock to the spread spectrum signal. By using spread spectrum techniques, such wireless alarm systems are highly reliable and provide a safety margin against jamming and undesirable interference. Other applications of spread spectrum techniques to commercial uses promise similar advantages in reliability in communications.
Methods for the serial search and acquisition of utilized spread spectrum frequencies are well known in the prior art, as shown in M. K. Simon et al., Spread Spectrum Communications, vol. 3, pp. 208-279, Rockville, Md.: Computer Science Press, 1985. In addition, M. K. Simon et al., supra at pp. 346-407 teach spread spectrum multiple access techniques such as utilizing ALOHA random access schemes.
A general object of the invention is to achieve superior jamming resistance compared to other spread spectrum means.
Another object of the invention is to allow multiple systems to co-exist without undesirable co-interference.
Another object of the invention is to minimize the effects of data collisions when a system supports numerous non-synchronized ALOHA protocol transmitters.
An additional object of the invention is to operate within the radio band allowed by the FCC with minimal cost and minimal frequency setting components.
A further object of the invention is to provide techniques suitable for a high level of monolithic circuit integration.
According to the present invention, as embodied and broadly described herein, a frequency agile method is provided which has a low cost solution to many burst mode and continuous data communications applications, including security systems, fire systems, access control, energy management, remote control of model planes, remote process control, traffic light control, remote power meter reading, voice communication, radio location, or other local area networks.
In remote monitoring applications, the frequency agile radio system typically includes one or more centrally located data collection receivers with one or more remotely located transmitters. In control applications, one or more centrally located transmitters may communicate with a plurality of remotely located receivers. Further, the system can provide two-way polled type communications where each data node requires both a receiver and a transmitter.
The method for providing frequency agility includes using a frequency agile transmitter and a frequency-agile radio system for sending a message-data signal by selecting a single pseudo-random frequency on which to transmit, by generating a preamble signal on a single carrier frequency for modulating message-data, by transmitting the preamble signal for a pre-set preamble time for allowing an appropriate frequency-agile receiver to lock-on the preamble signal, and by modulating the preamble signal with the message-data signal to produce a modulated signal. The message-data signal is defined herein to be a signal having message-data.
In addition, the method for providing frequency agility includes using a frequency-agile receiver in the frequency-agile radio system for avoiding occupied radio-frequency channels in a radio spectrum by scanning the radio spectrum, identifying occupied portions of the radio spectrum, updating information identifying the occupied portions, storing the updated information in memory means, associating a time-out period with the stored occupied portions, and skipping over the occupied portions of the radio spectrum during the time-out period in response to the information and while receiving with the frequency-agile receiver, so that only a single time counter is required for all radio bands.
Additional objects and advantages of the invention are set forth in part in the description which follows, and in part are obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention also may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.